A world of genetic diversity within a single tree

By Ed Yong | August 12, 2012 12:00 pm

Words like “individual” are hard to use when it comes to the black cottonwood tree. Each tree can sprout a new one that’s a clone of the original, and still connected by the same root system. This “offspring” is arguably the same tree – the same “individual” – as the “parent”. This semantic difficulty gets even worse when you consider their genes. Even though the parent and offspring are clones, it turns out that they have stark genetic differences between them.

It gets worse: when Brett Olds sequenced tissues from different parts of the same black cottonwood, he found differences in thousands of genes between the topmost bud, the lowermost branch, and the roots. In fact, the variation within a single tree can be greater than that across different trees.

As Olds told me, “This could change the classic paradigm that evolution only happens in a population rather than at an individual level.” There are uncanny parallels here to a story about cancer that I wrote last year, in which British scientists showed that a single tumour can contain a world of diversity, with different parts evolving individually from one another.

I learned about Olds’ study at the Ecological Society of America Annual Meeting and wrote about it for Nature. Head over there for the details.

Photo by Born1945

CATEGORIZED UNDER: Evolution, Genetics, Genomics, Plants

Comments (3)

  1. jd

    While Olds’ work showing just how much diversity is within a single tree, I think he may be overstating his case a bit by his “change the classic paradigm” statement. I was taught back in the early 90s in my Intro. Botany class that even though cuttings and reproduction via vegetative growth were spoken of as clones, in reality any plant that can vegetatively reproduce itself should be considered a population in its own right. My botany and ecology instructors did not know the degree to which the DNA changed during vegetative growth, but they knew that it did. The fact that plant genetics is so fiendishly complex is one of the big reasons why I went the zoological route:) Still, in this day and age, I don’t blame him for trying to sell the importance of his work.

  2. I’ve wondered how long-lived individual organisms like a redwood tree can survive assaults by species like bacteria/fungus/insects that can evolve through thousands of generations in the same time frame. The evolutionary arms race that’s so familiar in biology has one contestant frozen while the other can improve.

    Maybe this research represents a partial answer to that question.

  3. Isabel

    Agree with jd- this is not news. Just doing the whole genome and trying to quantify it in this species may be new, which is fine. But these things are common place in botany. Asexual reproduction is extremely common in non-animals and there have been many debates about what constitutes an individual, etc. I have even heard this exact story, that trees are very different genetically, even that flowers from opposite ends of a tree can no longer reproduce sexually because they have diverged too much. In plants reproductive tissue arises from somatic tissue throughout the organisms life, very unlike animals.

    What’s harder to explain is that tissues at the tip of a tree would be most similar and other strange findings mentioned in your other post.


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